Nitric oxide mediates interleukin-1 induced inhibition of glycosaminoglycan synthesis in rat articular cartilage

The relationship of ischemia-modified albumin levels to disease activity scores and HLA-B27 in patients with ankylosing spondylitis

OBJECTIVE:

Recent studies have implicated increased oxidative stress in the pathogenesis of Ankylosing spondylitis (AS). Ischemia-modified albumin (IMA), an altered form of albumin, increases oxidative stress. This study aimed to investigate the relationship between IMA levels and other indicators of disease severity in AS.

METHODS:

This study included 63 AS patients and 48 healthy controls. Patients were examined for serum lipid profile, C-reactive protein (CRP), complete blood count, Bath Ankylosing Spondylitis Disease Activity Index, human leukocyte antigen (HLA) B27, and treatment regimen. They were categorized based on disease activity, HLA-B27 status, and the drug treatment and compared for IMA levels.

RESULTS:

The patients had significantly higher IMA levels than controls (p=0.020); among patients, the levels were higher in those with active disease (p=0.001) and positively correlated with the CRP levels. No significant difference was found between the IMA levels of the patients with different HLA-B27 status or treatment method.

CONCLUSION:

The IMA levels were higher in patients than controls and further increased in patients with active AS. IMA was associated with disease activity and can be used as an inflammatory marker in AS. More comprehensive future studies with a larger sample size may help understand the relationship in greater detail.

Platelet-Rich Plasma Released From Polyethylene Glycol Hydrogels Exerts Beneficial Effects on Human Chondrocytes

Osteoarthritis (OA) is a debilitating joint disease resulting from chronic joint inflammation and erosion of articular cartilage. A promising biological treatment for OA is intra-articular administration of platelet-rich plasma (PRP). However, immediate bolus release of growth factors limits beneficial therapeutic effects of PRP, thus necessitating the demand for sustained release platforms. In this study, we evaluated the therapeutic value of PRP released from a polyethylene glycol (PEG) hydrogel on articular chondrocytes/cartilage explants derived from OA patients. Lyophilized PRP (PRGF) was encapsulated in PEG hydrogels at 10% w/v and hydrogel swelling, storage modulus and degradation and PRGF release kinetics were determined. PRGF releasate from the hydrogels was collected on day 1, 4, and 11. Encapsulation of PRGF at 10% w/v in PEG hydrogels had minimal effect on hydrogel properties. PRGF was released with an initial burst followed by sustained release until complete hydrogel degradation. Effect of PRGF releasates and bolus PRGF (1% w/v PRGF) on patient-derived cartilage explants or chondrocytes was assessed by chondrocyte proliferation (pico-green assay), gene expression for COL1A1, COL2A1, MMP13, COX2, and NFKB1 (real-time polymerase chain reaction), and measurement of nitric oxide concentration (Griess' assay). Compared to bolus PRGF, PRGF releasates enhanced chondrocyte proliferation, suppressed the expression of genes like MMP13, NFKB1, COL1A1, and COL2A1 and reduced levels of nitric oxide. Taken together, these results indicate that release of PRGF from PEG hydrogels may improve the therapeutic efficacy of PRP and merits further investigation in an animal model of OA. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:2401-2410, 2019.

Pentosan polysulfate inhibits IL-1β-induced iNOS, c-Jun and HIF-1α upregulation in canine articular chondrocytes

Osteoarthritic (OA) chondrocytes are shown to express inducible nitric oxide synthase (iNOS) which produces high concentrations of nitric oxide (NO), particularly when stimulated with proinflammatory cytokines. NO is involved in OA cartilage degradation. On the other hand, c-Jun N-terminal Kinase (JNK) pathway mediates the activation and transcription of c-Jun, which is required for interleukin-1 (IL-1)-induction of matrix metalloproteinases-13 (MMP-13) in OA pathogenesis. Therefore, the selective inhibition of iNOS and c-Jun is a promising target for treatment and prevention of OA. The purpose of the study was to investigate the inhibitory effects of pentosan polysulfate (PPS) on IL-1β-induced iNOS, c-Jun and HIF-α isoforms upregulation in canine articular chondrocytes (CACs). Primary (P0) chondrocytes were isolated and cultured from femoral head cartilages of three (3) dogs. First passage (P1) chondrocytes were preincubated with 0, 1, 5, 15 and 40 μg/mL of PPS for 4 hr before treatment with 10 ng/mL rhIL-1β for a further 8 hr. In addition, we evaluated the effects of single and multiple cytokine with or without LPS on iNOS protein induction. PPS significantly inhibited (P < 0.05) IL-1β-induced iNOS, c-Jun and HIF-1α mRNA upregulation in a dose-dependent pattern. iNOS mRNA was significantly inhibited at 15 and 40 μg/mL whereas c-Jun and HIF-1α were significantly downregulated at 5, 15 and 40 μg/mL of PPS compared to chondrocytes treated with only rhIL-1β. Intriguingly, CACs were recalcitrant to single IL-1β, TNF-α or LPS-induction of iNOS protein including to a combination of IL-1β+TNF-α, IL-1β+LPS except to TNF-α+LPS and IL-1β+TNF-α+LPS suggestive of a protective mechanism from iNOS detrimental effects on perpetuating OA. IL-1β+TNF-α+LPS-induced iNOS protein expression was significantly abrogated by PPS. We demonstrate for the first time that PPS is a novel inhibitor of IL-1β-induced iNOS, c-Jun, and HIF-1α mRNA upregulation and iNOS protein induction which may be beneficial for prevention and treatment OA.

Nitric oxide-associated chondrocyte apoptosis in trauma patients after high-energy lower extremity intra-articular fractures

BACKGROUND

The primary goal of this study was to identify nitric oxide (NO)-induced apoptosis in traumatized chondrocytes in intra-articular lower extremity fractures and the secondary goal was to identify the timeline of NO-induced apoptosis after injury.

MATERIALS AND METHODS

This is a prospective collection of samples of human cartilage harvested at the time of surgery to measure apoptotic cell death and the presence of NO by immunohistochemistry. Three patients met the criteria for control subjects and eight patients sustained high-energy intra-articular fractures and were included in the study. Subjects who sustained intra-articular acetabular, tibial, calcaneal and talus fracture had articular cartilage harvested at the time of surgical intervention. All 8 patients underwent open reduction and internal fixation of the displaced intra-articular fractures. The main outcome measures were rate of apoptosis, degree of NO-induced apoptosis in chondrocytes, and the timeline of NO-induced apoptosis after high-energy trauma.

RESULTS

The percentage of apoptotic chondrocytes was higher in impacted samples than in normal cartilage (56 vs 4 %), confirming the presence of apoptosis after intra-articular fracture. The percentage of cells with NO was greater in apoptotic cells than in normal cells (59 vs 20 %), implicating NO-induction of apoptosis. The correlation between chondrocyte apoptosis and increasing time from injury was found to be -0.615, indicating a decreasing rate of apoptosis post injury.

CONCLUSIONS

The data showed the involvement of NO-induced apoptosis of chondrocytes after high-energy trauma, which decreased with time from injury.

Chondroprotective and anti-inflammatory effects of S-methylisothiourea, an inducible nitric oxide synthase inhibitor in cartilage and synovial explants model of osteoarthritis

Objectives

To study the chondroprotective and anti-inflammatory potential of inducible nitric oxide synthase (iNOS) inhibitor S-methylisothiourea (SMT) in in-vitro model.

Methods

Rabbit cartilage explants were stimulated with recombinant human interleukin 1β (rhIL-1β), and the chondroprotective and anti-inflammatory effects of SMT were investigated. Rat synovial explants were stimulated with LPS, and the anti-inflammatory effect of SMT on synovium was studied. To examine the role of SMT in synovial inflammation mediated cartilage damage, LPS stimulated synovial explants were cultured with dead cartilage with or without SMT for 72 h. The culture medium was analysed for sulfated glycosaminoglycans (GAGs) and hydroxyproline as measure of proteoglycans and collagen degradation, respectively.

Key findings

SMT significantly reduced GAGs, hydroxyproline, matrix metalloproteinase (MMP)-13, tumour necrosis factor alpha (TNF-α), prostaglindin E2 (PGE2) and nitrite release in stimulated rabbit cartilage media indicating chondroprotective and anti-inflammatory effects of SMT in osteoarthritis (OA). Stimulated synovial explants caused release of nitrite, PGE2, IL-1β and TNF-α in the medium which were significantly reduced by SMT indicating its anti-inflammatory action. SMT significantly reduced GAGs and hydroxyproline in medium and shown protective effect against synovium-mediated cartilage damage.

Conclusions

SMT inhibited cartilage degradation, synovial inflammation and synovium-mediated cartilage damage, suggesting that SMT may be an agent for pharmacological intervention in OA.

Nitric oxide modulators: an emerging class of medicinal agents

Nitric oxide, a unique messenger in biological system, is ubiquitously present virtually in all tissues revealing its versatile nature of being involved in diverse physiological functions such as vascular tone, inhibition of platelet aggregation, cell adhesion, neurotransmission and enzyme and immune regulation. The tremendous advancements made in the past few decades in this area suggests that the nitric oxide modulation either by its exogenous release through nitric oxide donors or inhibition of its synthesis by nitric oxide synthase inhibitors in physiological milieu may provide newer clinical strategies for the treatment of some diseases. In this review, an attempt is made to document and understand the biological chemistry of different classes of nitric oxide modulators that would prove to be a fruitful area in the years to come.

Key Pathways to Prevent Posttraumatic Arthritis for Future Molecule-Based Therapy

Joint injuries are common, especially among young adults aged 18 to 44 years. They are accompanied by a cascade of events that increase the risk of posttraumatic osteoarthritis (PTOA). Therefore, understanding of biological responses that predispose to PTOA should help in determining treatment modalities to delay and/or prevent the onset and progression of the disease. The vast majority of the literature pointed to chondrocyte death and apoptosis, inflammation and matrix damage/fragmentation being the earliest events that follow joint trauma. Together these events lead to the development of osteoarthritis-like focal cartilage lesions that if untreated have a tendency to expand and progress to fully developed disease. Currently, the only treatments available for joint trauma are surgical interventions. Experimental biologic approaches involve engineering of cartilage with the use of cells (stem cells or chondrocytes), juvenile or adult cartilage pieces, scaffolds, and various polymeric matrices. The major challenge for all of them is regeneration of normal functional mature hyaline cartilage that can sustain the load, resist compression, and most important, integrate with the host tissue. If the tissue is spontaneously repaired it fails to reproduce original structure and function and thus, may be more susceptible to re-injury. Thus, there is a critical need to develop novel molecular mechanism-based therapeutic approaches to biologic chondral and/or osteochondral repair. The focus of this review is on the earliest molecular and cellular manifestations of injury that can be grouped based on the following therapeutic options for PTOA: chondroprotection, anti-inflammatory, matrix protection, and matrix remodeling/matrix synthesis.

Nitric oxide as a mediator of inflammation?-You had better believe it

Nitric oxide has enigmatic qualities in inflammation. In order to appreciate the precise contributions of nitric oxide to a pathophysiological process, one must account for enzyme source, coproduction of oxidants and antioxidant defences, time, rate of nitric oxide production, cellular source, peroxynitrite formation and effects on DNA (mutagenesis/apoptosis). We contend that there is ample evidence to consider nitric oxide as a molecular aggressor in inflammation, particularly chronic inflammation. Therapeutic benefit can be achieved by inhibition of inducible nitric oxide synthase and not the donation of additional nitric oxide. Furthermore, there is growing appreciation that nitric oxide and products derived thereof, are critical components linking the increased incidence of cancer in states of chronic inflammation.

Painful decisions for senior pets

Osteoarthritis and cancer are the inevitable consequences of aging and significantly contribute to the cause of death in cats and dogs. Managing the pain associated with these disease states is the veterinarian’s mandate. Many treatment modalities and agents are available for patient management; however, it is only with an understanding of disease neurobiology and a mechanism-based approach to problem diagnosis that the clinician can offer patients an optimal quality of life based on evidence-based best medicine. When treating pain, knowledge is still our best weapon.

Platelet-rich plasma releasate inhibits inflammatory processes in osteoarthritic chondrocytes

BACKGROUND

Platelet-rich plasma (PRP) has recently been postulated as a treatment for osteoarthritis (OA). Although anabolic effects of PRP on chondrocytes are well documented, no reports are known addressing effects on cartilage degeneration. Since OA is characterized by a catabolic and inflammatory joint environment, the authors investigated whether PRP was able to counteract the effects of such an environment on human osteoarthritic chondrocytes.

HYPOTHESIS

Platelet-rich plasma inhibits inflammatory effects of interleukin-1 (IL-1) beta on human osteoarthritic chondrocytes.

STUDY DESIGN

Controlled laboratory study.

METHODS

Human osteoarthritic chondrocytes were cultured in the presence of IL-1 beta to mimic an osteoarthritic environment. Medium was supplemented with 0%, 1%, or 10% PRP releasate (PRPr, the active releasate of PRP). After 48 hours, gene expression of collagen type II alpha 1 (COL2A1), aggrecan (ACAN), a disintegrin and metalloproteinase with thrombospondin motifs (ADAMTS)4, ADAMTS5, matrix metalloproteinase (MMP)13, and prostaglandin-endoperoxide synthase (PTGS)2 was analyzed. Additionally, glycosaminoglycan (GAG) content, nitric oxide (NO) production, and nuclear factor kappa B (NFκB) activation were studied.

RESULTS

Platelet-rich plasma releasate diminished IL-1 beta-induced inhibition of COL2A1 and ACAN gene expression. The PRPr also reduced IL-1 beta-induced increase of ADAMTS4 and PTGS2 gene expression. ADAMTS5 gene expression and GAG content were not influenced by IL-1 beta or additional PRPr. Matrix metalloproteinase 13 gene expression and NO production were upregulated by IL-1 beta but not affected by added PRPr. Finally, PRPr reduced IL-1 beta-induced NFκB activation to control levels containing no IL-1 beta.

CONCLUSION

Platelet-rich plasma releasate diminished multiple inflammatory IL-1 beta-mediated effects on human osteoarthritic chondrocytes, including inhibition of NFκB activation.

CLINICAL RELEVANCE

Platelet-rich plasma releasate counteracts effects of an inflammatory environment on genes regulating matrix degradation and formation in human chondrocytes. Platelet-rich plasma releasate decreases NFκB activation, a major pathway involved in the pathogenesis of OA. These results encourage further study of PRP as a treatment for OA.

Cellular and molecular mechanisms of anti-inflammatory effect of Aflapin: a novel Boswellia serrata extract

There is significant number of evidences suggesting the anti-inflammatory properties of gum resin extracts of Boswellia serrata containing 3-O-acetyl-11-keto-β-boswellic acid (AKBA) and their promising potential as therapeutic interventions against inflammatory diseases such as osteoarthritis (OA). Unfortunately, the poor bioavailability of AKBA following oral administration might limit the anti-inflammatory efficacy of standardized Boswellia extract(s). To address this issue, we describe a novel composition called Aflapin, which contains B. serrata extract enriched in AKBA and non-volatile oil portion of B. serrata gum resin. Our observations show that the availability of AKBA in systemic circulation of experimental animals is increased by 51.78% in Aflapin-supplemented animals, in comparison with that of 30% AKBA standardized extract or BE-30 (5-Loxin(®)). Consistently, Aflapin confers better anti-inflammatory efficacy in Freund's Complete Adjuvant (FCA)-induced inflammation model of Sprague-Dawley rats. Interestingly, in comparison with BE-30, Aflapin(®) also provides significantly better protection from IL-1β-induced death of human primary chondrocytes and improves glycosaminoglycans production in human chondrocytes. In Tumor necrosis factor alpha (TNFα)-induced human synovial cells, the inhibitory potential of Aflapin (IC(50) 44.736 ng/ml) on matrix metalloproteinase-3 (MMP-3) production is 14.83% better than that of BE-30 (IC(50) 52.528 ng/ml). In summary, our observations collectively suggest that both the Boswellia products, BE-30 (5-Loxin(®)) and Aflapin, exhibit powerful anti-inflammatory efficacy and anti-arthritic potential. In particular, in comparison with BE-30, Aflapin provides more potential benefits in recovering articular cartilage damage or protection from proteolytic degradation due to inflammatory insult in arthritis such as osteoarthritis or rheumatoid arthritis.

Effect of oleocanthal and its derivatives on inflammatory response induced by lipopolysaccharide in a murine chondrocyte cell line

OBJECTIVE

In joint diseases, cartilage homeostasis is disrupted by mechanisms that are driven by combinations of biologic factors that vary according to the disease process. In osteoarthritis (OA), biomechanical stimuli predominate, with up-regulation of both catabolic and anabolic factors. Likewise, OA progression is characterized by increased nitric oxide (NO) production, which has been associated with cartilage degradation. Given the relevance of cartilage degenerative diseases in our society, the development of a novel pharmacologic intervention is a critically important public health goal. Recently, oleocanthal isolated from extra virgin olive oil was found to display nonsteroidal antiinflammatory drug activity similar to that of ibuprofen, a drug widely used in the therapeutic management of joint inflammatory diseases. We undertook this study to evaluate the effect of oleocanthal and its derivatives on the modulation of NO production in chondrocytes.

METHODS

Cultured ATDC-5 chondrocytes were tested with different doses of oleocanthal and its derivatives. Cell viability was evaluated using the MTT assay. Nitrite accumulation was determined in culture supernatant using the Griess reaction. Inducible NO synthase (NOS2) protein expression was examined using Western blotting analysis.

RESULTS

Oleocanthal and its derivatives decreased lipopolysaccharide-induced NOS2 synthesis in chondrocytes without significantly affecting cell viability at lower concentrations. Among the derivatives we examined, derivative 231 was the most interesting, since its inhibitory effect on NOS2 was devoid of cytotoxicity even at higher concentrations.

CONCLUSION

This class of molecules shows potential as a therapeutic weapon for the treatment of inflammatory degenerative joint diseases.

Leptin enhances synthesis of proinflammatory mediators in human osteoarthritic cartilage--mediator role of NO in leptin-induced PGE2, IL-6, and IL-8 production

Obesity is an important risk factor for osteoarthritis (OA) in weight-bearing joints, but also in hand joints, pointing to an obesity-related metabolic factor that influences on the pathogenesis of OA. Leptin is an adipokine regulating energy balance, and it has recently been related also to arthritis and inflammation as a proinflammatory factor. In the present paper, the effects of leptin on human OA cartilage were studied. Leptin alone or in combination with IL-1 enhanced the expression of iNOS and COX-2, and production of NO, PGE₂, IL-6, and IL-8. The results suggest that the effects of leptin are mediated through activation of transcription factor nuclear factor κB (NF-κB) and mitogen-activated protein kinase (MAPK) pathway c-Jun NH₂-terminal kinase (JNK). Interestingly, inhibition of leptin-induced NO production with a selective iNOS inhibitor 1400 W inhibited also the production of IL-6, IL-8, and PGE₂, and this was reversed by exogenously added NO-donor SNAP, suggesting that the effects of leptin on IL-6, IL-8, and PGE₂ production are dependent on NO. These findings support the idea of leptin as a factor enhancing the production of proinflammatory factors in OA cartilage and as an agent contributing to the obesity-associated increased risk for osteoarthritis.

The role of nitric oxide in osteoarthritis

Elevated levels of markers of nitric oxide (NO) production are found in osteoarthritic joints suggesting that NO is involved in the pathogenesis of osteoarthritis (OA). In OA, NO mediates many of the destructive effects of interleukin-1 (IL-1) and tumour necrosis factor-alpha (TNF-alpha) in the cartilage, and inhibitors of NO synthesis have demonstrated retardation of clinical and histological signs and symptoms in experimentally induced OA and other forms of arthritis. As an important factor in cartilage, the regulation of inducible nitric oxide synthase (iNOS) expression and activity, and the effects of NO are reviewed, especially in relation to the pathogenesis of OA.

Protective effects of total fraction of avocado/soybean unsaponifiables on the structural changes in experimental dog osteoarthritis: inhibition of nitric oxide synthase and matrix metalloproteinase-13

INTRODUCTION

The aims of this study were, first, to investigate the in vivo effects of treatment with avocado/soybean unsaponifiables on the development of osteoarthritic structural changes in the anterior cruciate ligament dog model and, second, to explore their mode of action.

METHODS

Osteoarthritis was induced by anterior cruciate ligament transection of the right knee in crossbred dogs. There were two treatment groups (n = 8 dogs/group), in which the animals received either placebo or avocado/soybean unsaponifiables (10 mg/kg per day), which were given orally for the entire duration of the study (8 weeks). We conducted macroscopic and histomorphological analyses of cartilage and subchondral bone of the femoral condyles and/or tibial plateaus. We also conducted immunohistochemical analyses in cartilage for the following antigens: inducible nitric oxide synthase, matrix metalloproteinase (MMP)-1, MMP-13, a disintegrin and metalloproteinase domain with thrombospondin motifs (ADAMTS)4 and ADAMTS5.

RESULTS

The size of macroscopic lesions on the tibial plateaus was decreased (P = 0.04) in dogs treated with the avocado/soybean unsaponifiables. Histologically, in these animals the severity of cartilage lesions on both tibial plateaus and femoral condyles, and the cellular infiltration in synovium were significantly decreased (P = 0.0002 and P = 0.04, respectively). Treatment with avocado/soybean unsaponifiables also reduced loss of subchondral bone volume (P < 0.05) and calcified cartilage thickness (P = 0.01) compared with placebo. Immunohistochemical analysis of cartilage revealed that avocado/soybean unsaponifiables significantly reduced the level of inducible nitric oxide synthase (P < 0.05) and MMP-13 (P = 0.01) in cartilage.

CONCLUSIONS

This study demonstrates that treatment with avocado/soybean unsaponifiables can reduce the development of early osteoarthritic cartilage and subchondral bone lesions in the anterior cruciate ligament dog model of osteoarthritis. This effect appears to be mediated through the inhibition of inducible nitric oxide synthase and MMP-13, which are key mediators of the structural changes that take place in osteoarthritis.

Aurothiomalate and hydroxychloroquine inhibit nitric oxide production in chondrocytes and in human osteoarthritic cartilage

OBJECTIVES

Nitric oxide (NO) is a destructive mediator produced by activated chondrocytes. The aim of the present study was to investigate the effect of disease-modifying anti-rheumatic drugs (DMARDs) on interleukin-1beta (IL-1beta)-induced NO production in chondrocyte cultures, and in human osteoarthritic cartilage.

RESULTS

Aurothiomalate, hydroxychloroquine, methotrexate and leflunomide inhibited IL-1beta-induced inducible NO synthase (iNOS) expression and NO production in immortalized H4 chondrocytes, while penicillamine and sulfasalazine had no effect. This can be explained by the fact that the four effective DMARDs also suppressed IL-1beta-induced activation of nuclear factor kappa B (NF-kappaB), which is a crucial transcription factor for iNOS. Aurothiomalate and hydroxychloroquine also inhibited IL-1beta-induced NO production in OA cartilage whereas methotrexate and leflunomide had no effect.

CONCLUSION

Aurothiomalate and hydroxychloroquine suppressed IL-1beta-induced NO production in chondrocyte cultures and in OA cartilage. The results suggest an additional anti-inflammatory mechanism for aurothiomalate and hydroxychloroquine and indicates their possible therapeutic value in the treatment of osteoarthritis (OA).

Integrin-mediated mechanotransduction in IL-1 beta stimulated chondrocytes

Mechanical loading and interleukin-1 beta (IL-1 beta) influence the release of nitric oxide (*NO) and prostaglandin E2 (PGE2) from articular chondrocytes via distinct signalling mechanisms. The exact nature of the interplay between the respective signalling pathways remains unclear. Recent studies have shown that integrins act as mechanoreceptors and may transduce extracellular stimuli into intracellular signals, thereby influencing cellular response. The current study demonstrates that the application of dynamic compression induced an inhibition of *NO and an upregulation of cell proliferation and proteoglycan synthesis in the presence and absence of IL-1 beta. PGE2 release was not affected by dynamic compression in the absence of IL-1 beta but was inhibited in the presence of the cytokine. The integrin binding peptide, GRGDSP, abolished or reversed the compression-induced alterations in all four parameters assessed in the presence and absence of IL-1 beta. The non-binding control peptide, GRADSP, had no effect. These data clearly demonstrate that the metabolic response of the chondrocytes to dynamic compression in the presence and absence of IL-1 beta, are integrin mediated.

Octacalcium phosphate crystals directly stimulate expression of inducible nitric oxide synthase through p38 and JNK mitogen-activated protein kinases in articular chondrocytes

Basic calcium phosphate (BCP) crystals, including hydroxyapatite, octacalcium phosphate (OCP) and carbonate-apatite, have been associated with severe osteoarthritis and several degenerative arthropathies. Most studies have considered the chondrocyte to be a bystander in the pathogenesis of calcium crystal deposition disease, assuming that synovial cell cytokines were the only triggers of chondrocyte activation. In the present study we identified direct activation of articular chondrocytes by OCP crystals, which are the BCP crystals with the greatest potential for inducing inflammation. OCP crystals induced nitric oxide (NO) production and inducible nitric oxide synthase (NOS) mRNA expression by isolated articular chondrocytes and cartilage fragments, in a dose-dependent manner and with variations over time. OCP crystals also induced IL-1β mRNA expression. Using pharmacological and cytokine inhibitors, we observed that OCP crystals induced NO production and inducible NOS mRNA activation were regulated at both the transcriptional and the translational levels; were independent from IL-1β gene activation; and involved p38 and c-Jun amino-terminal kinase (JNK) mitogen-activated protein kinase (MAPK) pathways, as further confirmed by OCP crystal-induced p38 and JNK MAPK phosphorylation. Taken together, our data suggest that the transcriptional inducible NOS response to OCP crystals involved both the p38 and the JNK MAPK pathways, probably under the control of activator protein-1. NO, a major mediator of cartilage degradation, can be directly produced by BCP crystals in chondrocytes. Together with synovial activation, this direct mechanism may be important in the pathogenesis of destructive arthropathies triggered by microcrystals.

Oral treatment with PD-0200347, an ?2? ligand, reduces the development of experimental osteoarthritis by inhibiting metalloproteinases and inducible nitric oxide synthase gene expression and synthesis in cartilage chondrocytes

OBJECTIVE

To examine the in vivo effects of PD-0200347, an alpha(2)delta ligand of voltage-activated Ca(2+) channels and a compound chemically related to pregabalin and gabapentin, on the development of cartilage structural changes in an experimental dog model of osteoarthritis (OA). The effects of PD-0200347 on the major pathways involved in OA cartilage degradation, including matrix metalloproteinases (MMPs) and the inducible form of nitric oxide synthase (iNOS), were also studied.

METHODS

OA was surgically induced in dogs by sectioning the anterior cruciate ligament. OA dogs were randomly distributed into 3 groups and treated orally with either 1) placebo, 2) 15 mg/kg/day of PD-0200347, or 3) 90 mg/kg/day of PD-0200347. Dogs were killed 12 weeks after surgery. The severity of the lesions was scored macroscopically and histologically. Cartilage specimens from the femoral condyles and tibial plateaus were processed for RNA extraction and quantitative reverse transcription-polymerase chain reaction (RT-PCR) or immunohistochemistry. Specific probes and antibodies were used to study the messenger RNA and protein levels of iNOS, MMP-1, MMP-3, and MMP-13.

RESULTS

No clinical signs of drug toxicity were noted in the treated animals. Treatment with PD-0200347 at both dosages tested (15 and 90 mg/kg/day) reduced the development of cartilage lesions. There was a reduction in the score of lesions, with a statistically significant (P = 0.01) difference when the highest dosage of the drug was administered. The reduction in the score was mainly related to a decrease in the surface size of the lesions. Quantitative RT-PCR showed that PD-0200347 significantly reduced the expression of MMP-13, a key mediator in OA. Immunohistochemical analyses showed that treatment with PD-0200347 significantly reduced the synthesis of all key OA mediators studied.

CONCLUSION

This study demonstrated the efficacy of PD-0200347 in reducing the progression of cartilage structural changes in a dog model of OA. It also showed that this effect is linked to the inhibition of the major pathophysiologic mediators responsible for cartilage degradation.

Disposition and pharmacokinetics of L-N6-(1-iminoethyl)lysine-5-tetrazole-amide, a selective iNOS inhibitor, in rats

The metabolism, pharmacokinetics, tissue distribution, and excretion of L-N6-(1-iminoethyl)lysine-5-tetrazole-amide (L-NIL-TA), a selective inducible NO synthase (iNOS) inhibitor, were investigated in rats. [(14)C]L-NIL-TA is extensively metabolized after either oral or IV administration with a minor amount (<1%) excreted as the prodrug. L-NIL-TA is metabolized via a single hydrolysis pathway to form the active drug, L-N6-(1-iminoethyl)lysine (L-NIL). The oxidative deamination of 2-amino group of L-NIL forms a 2-keto metabolite (M5), which further loses carbon dioxide to yield a carboxylic acid metabolite (M6). Acetylation of L-NIL and M5 resulted in the formations of metabolites M7 and M4, respectively. Complete recovery of the radioactive dose was achieved after either oral (91.2% in urine and 4.66% in feces) and IV (99.3% in urine and 5.11% in feces) administration. L-NIL-TA-related material was extensively distributed to the tissues, with the highest concentration of radioactivity being found in muscle. Maximal concentration of radioactivity was reached between 0.5 and 1 h post-dose in the majority of tissues, with the exception of muscle and skin where the maximal concentrations were achieved at 8 h post-dose.

Regulation of nitric oxide production in osteoarthritic and rheumatoid cartilage. Role of endogenous IL-1 inhibitors

OBJECTIVE

To investigate the endogenous regulation of interleukin-1 (IL-1) cytokine network in osteoarthritic (OA) and rheumatoid (RA) cartilage in relation to nitric oxide (NO) production.

METHODS

Cartilage specimen obtained from OA and RA patients undergoing knee replacement surgery were studied for iNOS expression, NO and IL-1 antagonist production in tissue culture.

RESULTS

OA cartilage responded to IL-1beta-stimulation with higher NO production than RA cartilage, whereas there was no difference in NO synthesis between OA and RA samples when stimulated by TNFalpha or LPS. Interleukin-1 receptor antagonist (IL-1Ra) production was higher in RA cartilage than in OA cartilage, and its production was increased by NO synthase inhibitor 1400W.

CONCLUSION

IL-1beta is a potent stimulator of NO production by the iNOS pathway in RA and more pronouncedly in OA cartilage. This process is regulated by cartilage derived IL-1 antagonists, and is implicated in cartilage destruction and synovial inflammation in OA and RA joints.

The in situ up-regulation of chondrocyte interleukin-1-converting enzyme and interleukin-18 levels in experimental osteoarthritis is mediated by nitric oxide

OBJECTIVE

To investigate in situ the relationship between 2 key mediators implicated in osteoarthritic (OA) cartilage: nitric oxide (NO) and interleukin-1-converting enzyme (ICE). Interleukin-18 (IL-18) was also studied and served as reference for the effects of ICE.

METHODS

An OA model was created in dogs by sectioning (stab wound) the anterior cruciate ligament of the right stifle joint. Three experimental groups were studied: unoperated untreated dogs, operated untreated dogs (OA), and OA dogs treated with oral N-iminoethyl-L-lysine (L-NIL), a specific inhibitor of inducible nitric oxide synthase (iNOS) (10 mg/kg twice a day starting immediately after surgery). At 12 weeks after surgery, cartilage from the femoral condyles and tibial plateaus were processed for immunohistochemistry for ICE, IL-18, and protease inhibitor 9 (PI-9), a natural inhibitor of ICE, followed by morphometric analysis. Cartilage specimens from the femoral condyles of untreated OA dogs were dissected and incubated with specific inhibitors of different signaling pathways likely to be involved in the OA process: SB 202190 (10 microM; a p38 mitogen-activated protein kinase [MAPK] inhibitor), PD 98059 (100 microM; a MAPK kinase 1/2 [MEK-1/2] inhibitor), NS-398 (10 ng/ml; a specific cyclooxygenase 2 [COX-2] inhibitor), and L-NIL (50 microM).

RESULTS

Both ICE and IL-18 were present in situ in the canine cartilage, with a significant increase in the level of these 2 proteins in OA cartilage. In contrast, the level of PI-9 was lower in OA than in normal cartilage (difference not statistically significant). Compared with untreated OA cartilage, oral treatment with L-NIL significantly decreased ICE and IL-18 levels in cartilage from the femoral condyles and tibial plateaus, to values similar to those in normal dogs. L-NIL also increased the PI-9 level in normal dogs compared with OA dogs, reaching statistical significance for femoral condyle cartilage. Interestingly, in vitro experiments demonstrated significant inhibition of ICE levels by p38, MEK-1/2, and COX-2 inhibitors, but not by the iNOS inhibitor.

CONCLUSION

This study demonstrated that in situ in OA cartilage, the stimulation of chondrocytes by NO is at least partly responsible for the up-regulation of ICE and IL-18 synthesis while decreasing the level of the ICE inhibitor PI-9. The ICE level is controlled by the activation of at least 2 MAPK pathways, p38 and MEK-1/2. Interestingly, it appears that ICE synthesis is not regulated by the endogenous production of NO. These data highlight the role played by iNOS in regulating the synthesis of major catabolic factors involved in OA cartilage degradation.

Effects of TNFalpha-antagonists on nitric oxide production in human cartilage

OBJECTIVE

Nitric oxide (NO) produced by cartilage and synovial membrane is implicated in the pathogenesis of osteoarthritis (OA) and rheumatoid arthritis (RA). In inflamed joints NO is synthesized in response to proinflammatory cytokines and it is involved in the joint destruction. The aim of the present study was to investigate the effects of TNFalpha-antagonists infliximab and etanercept on NO production in human cartilage.

DESIGN

Cartilage specimen obtained from OA patients undergoing knee replacement surgery were studied for iNOS expression and NO production in organ culture to allow intact chondrocyte-matrix interactions. TNFalpha and soluble TNFalpha receptor release was measured by ELISA.

RESULTS

Osteoarthritic cartilage produced NO spontaneously and its production was enhanced by proinflammatory cytokines TNFalpha (tumor necrosis factor alpha), IL-1beta (interleukin-1beta), IL-17 (interleukin-17) and by bacterial lipopolysaccharide (LPS). TNFalpha-antagonists infliximab and etanercept inhibited TNFalpha-induced NO production in a dose dependent manner but they had no effect on IL-1beta-, IL-17- and LPS-stimulated NO synthesis. TNFalpha and soluble TNFalpha receptors (sTNFRI and sTNFRII) were produced by human osteoarthritic cartilage. A neutralizing antibody against soluble TNFRI enhanced spontaneous NO production whereas an antibody against soluble TNFRII had no effect.

CONCLUSIONS

TNFalpha-antagonists infliximab and etanercept suppressed TNFalpha-induced NO production. This effect was not seen on IL-1-, IL-17- or LPS-induced NO production suggesting that TNFalpha is not an autacoid mediator in these processes. The studies with neutralizing antibodies against soluble TNFRI suggest that endogenous cartilage-derived TNFalpha-antagonists modulate NO production in osteoarthritic cartilage.

Recombinant equine interleukin-1beta induces putative mediators of articular cartilage degradation in equine chondrocytes

Interleukin-1 is considered a central mediator of cartilage loss in osteoarthritis in several species, however an equine recombinant form of this cytokine is not readily available for in vitro use in equine osteoarthritis research. Equine recombinant interleukin-1beta was cloned and expressed and its effects on the expression and activity of selected chondrocytic proteins implicated in cartilage matrix degradation were characterized. Reverse transcriptase polymerase chain reaction methods were used to amplify the entire coding region of the equine IL-1beta mRNA, which was cloned into an expression vector, expressed in E. coli, and purified using a Ni2+ chromatographic method. The effects of the recombinant peptide on chondrocyte gene expression were determined by Northern blotting using RNA from equine chondrocyte cultures hybridized to probes for matrix metalloproteinases (MMP 1, MMP 3, MMP 13), tissue inhibitor of matrix metalloproteinases 1 (TIMP 1) and cyclooxygenase 2 (COX 2). Effects on selected mediators of cartilage degradation (nitrite concentrations and MMP activity) were determined using conditioned medium from reIL-1beta-treated equine cartilage explant cultures. A recombinant peptide of approximately 21 kd was obtained. Northern blotting analyses revealed a marked up-regulation of expression of all MMPs, TIMP 1, and COX 2 in mRNA from treated chondrocytes. Furthermore, cartilage explants exposed to reIL-1beta had augmented collagenase/gelatinase and stromelysin activities as well as increased concentration of nitrite in conditioned media. The development of a biologically active, species-specific IL-1beta provides a valuable tool in the study of osteoarthritis pathophysiology and its treatment in horses.

Inducible nitric oxide expression in equine articular chondrocytes: effects of antiinflammatory compounds

OBJECTIVE

To determine the effects of recombinant equine IL-1beta and a number of antiinflammatory compounds on the expression and activity of inducible nitric oxide synthase (iNOS) in cultured equine chondrocytes.

DESIGN

RT-PCR methods were used to amplify a portion of the equine iNOS message to prepare an RNA probe. Northern blot analysis was used to quantify the expression of iNOS in first passage cultures of equine articular chondrocytes propagated in the presence or absence of recombinant equine interleukin-1beta (reIL-1beta), dexamethasone (DEX), polysulfated glycosaminoglycan (PSGAG), hyaluronan (HA), and phenylbutazone (PBZ), each at concentrations of 10 and 100 microg/ml. Nitrite concentrations in conditioned media of similarly treated cells were used to quantify iNOS activity.

RESULTS

Recombinant equine IL-1beta increased the expression of iNOS in a dose-dependent manner. This result was paralleled by an increased concentration of nitrite in the culture media of reIL-1beta-treated cells. DEX and PSGAG significantly reduced iNOS gene expression and media supernatant nitrite concentrations in cytokine-stimulated cultures. HA and PBZ had no consistent effect on the expression of iNOS and did not significantly influence nitrite content of conditioned media.

CONCLUSIONS

NO is considered an important mediator in the pathophysiologic processes of arthritis and an inducible NOS is expressed by equine chondrocytes. Pre-translational regulation of the iNOS gene by DEX and PSGAG appears to contribute to the cartilage-sparing properties of these compounds.

Regulation of the nitric oxide production resulting from the glucocorticoid-insensitive expression of iNOS in human osteoarthritic cartilage

OBJECTIVE

Nitric oxide (NO) produced by cartilage and synovial membranes is implicated in the pathogenesis of osteoarthritis (OA) and inhibitors of NO synthesis may have indications in the treatment or prevention of joint destruction in OA. Because the signaling mechanisms as well as the NOS isoform involved in induction of NO production in human cartilage remain in many parts unclear, the present study was designed to investigate the regulation of inducible NO synthesis in human intact OA cartilage.

METHODS

Cartilage specimens were collected from OA patients undergoing knee replacement surgery and studied for iNOS expression and NO production in organ culture to allow intact chondrocyte-matrix interactions. J774 macrophages were used for comparison as a well-documented source of iNOS.

RESULTS

OA cartilage expressed iNOS and produced NO in the absence of exogenous cytokines. Addition of interleukin-1 beta (IL-1 beta), tumor necrosis factor alpha (TNF alpha) or lipopolysaccharide (LPS) into the culture medium enhanced NO production in a dose-and time-dependent manner. Various NOS inhibitors suppressed NO production in the following order of potency: 1400W (novel selective iNOS inhibitor)=L-NIO>L-NMMA>L-NAME. Cycloheximide (an inhibitor of protein synthesis), pyrrolidine dithiocarbamate (PDTC; an NF-kappa B inhibitor) and genistein (an inhibitor of tyrosine protein kinases) inhibited cytokine-induced NO production, while dexamethasone, diaminohydroxypyrimidine (DAHP; an inhibitor of tetrahydrobiopterin synthesis) and PD 98059 (p42/44 MAP kinase inhibitor) had no effect.

CONCLUSIONS

The results suggest that NO synthesis in human osteoarthritic cartilage derives from the glucocorticoid-insensitive expression of iNOS. Very similar mechanisms appear to regulate inducible NO synthesis in human osteoarthritic cartilage and J774 macrophages with the exception that dexamethasone inhibited NO production in J774 cells but not in osteoarthritic cartilage.

Dynamic compression inhibits the synthesis of nitric oxide and PGE(2) by IL-1beta-stimulated chondrocytes cultured in agarose constructs

Both mechanical loading and interleukin-1beta (IL-1beta) are known to regulate metabolic processes in articular cartilage through pathways mediated by nitric oxide ((*)NO) and PGE(2). This study uses a well-characterized model system involving isolated chondrocytes cultured in agarose constructs to test the hypothesis that dynamic compression alters the synthesis of (*)NO and PGE(2) by IL-1beta-stimulated articular chondrocytes. The data presented demonstrate for the first time that dynamic compression counteracts the effects of IL-1beta on articular chondrocytes by suppressing both (*)NO and PGE(2) synthesis. Inhibitor experiments indicated that the dynamic compression-induced inhibition of PGE(2) synthesis and stimulation of proteoglycan synthesis were (*)NO mediated, while compression-induced stimulation of cell proliferation was (*)NO independent. The inhibition of (*)NO and PGE(2) by dynamic compression is a finding of major significance that could contribute to the development of novel strategies for the treatment of cartilage-degenerative disorders.

Inhibition by nitric oxide-releasing compounds of E-selectin expression in and neutrophil adhesion to human endothelial cells

The effects of two chemically unrelated nitric oxide (NO)-releasing compounds were studied on adhesion molecule expression in and neutrophil adhesion to human umbilical vein endothelial cells. Incubation of confluent monolayers of endothelial cells with increasing concentrations of lipopolysaccharide stimulated the adhesion of polymorphonuclear leukocytes to endothelial cells. Flow cytometric analysis showed that lipopolysaccharide treatment upregulated the expression of adhesion molecules E-selectin and intercellular adhesion molecule-1 (ICAM-1) in human umbilical vein endothelial cells. A novel NO-releasing compound GEA 3175 (1,2,3, 4-oxatriazolium, -3-(3-chloro-2-methylphenyl)-5-[[(4-methylphenyl)sulfonyl]amino]-, hydroxide inner salt) inhibited lipopolysaccharide-induced adhesion being more potent than the earlier known NO donor S-nitroso-N-acetylpenicillamine. The increased E-selectin expression induced by lipopolysaccharide was significantly attenuated by the two NO donors tested whereas ICAM-1 expression remained unaltered. The present data show that NO donors inhibit E-selectin expression in and neutrophil adhesion to lipopolysaccharide-stimulated vascular endothelial cells. Thus, by inhibiting leukocyte adhesion NO donors may reduce leukocyte infiltration and leukocyte-mediated tissue injury in inflammation and ischemia-reperfusion injury.

Does nitric oxide help explain the differential healing capacity of the anterior cruciate, posterior cruciate, and medial collateral ligaments?

This study compared the ability of rabbit medial collateral ligament, posterior cruciate ligament, and anterior cruciate ligament tissue to synthesize nitric oxide, and determined its effects on matrix synthesis, an important component of ligament repair. It is not known whether ligament cells can produce nitric oxide and, if so, whether it influences healing of ligament injuries. The anterior cruciate and posterior cruciate ligament tissue produced large amounts of nitric oxide in response to the inflammatory cytokine interleukin-1. Medial collateral ligament, in contrast, produced only modest amounts of nitric oxide. Furthermore, anterior cruciate ligament and, to some degree, posterior cruciate ligament synthesized nitric oxide spontaneously in culture, whereas medial collateral ligament never did so. When nitric oxide was supplied to these tissues, it strongly inhibited collagen synthesis by the two cruciate ligaments, but had little effect on collagen synthesis by the medial collateral ligament. Endogenously synthesized nitric oxide was also able to inhibit collagen synthesis as well as proteoglycan synthesis by the two cruciate ligaments, but had little effect on matrix synthesis by the medial collateral ligament. We propose a novel hypothesis, based on nitric oxide production and matrix synthesis, that may help explain why the two cruciate ligaments have such limited healing capacity compared with the medial collateral ligament.

Mitogen-activated protein kinase and nuclear factor kappaB together regulate interleukin-17-induced nitric oxide production in human osteoarthritic chondrocytes: possible role of transactivating factor mitogen-activated protein kinase-activated proten kinase (MAPKAPK)

OBJECTIVE

To explore the signaling pathways by which the proinflammatory cytokine interleukin-17 (IL-17) may contribute to cartilage catabolism in osteoarthritis (OA) by inducing inducible nitric oxide synthase (iNOS) expression in chondrocytes.

METHODS

We examined the IL-17-induced NO production in human OA chondrocytes, in combination with the proinflammatory cytokines IL-1beta, tumor necrosis factor alpha (TNF alpha), and leukemia inhibitory factor (LIF); the antiinflammatory cytokines IL-4, IL-10, and IL-13; and IL-1 receptor antagonist (IL-1Ra). Further, we explored the major intracellular signaling pathways through which IL-17 induced iNOS expression and NO production.

RESULTS

Treatment with IL-17 induced a dose-dependent increase in the level of NO. When IL-17 was combined with the above factors, it resulted in a synergistic effect with TNF alpha, an additive effect with LIF, and no further effect than when used alone with IL-1beta. IL-4, IL-10, IL-13, and IL-1Ra had no true effect on IL-17-induced NO production. The cAMP mimetics, 3-isobutyl-1-methyl xanthine plus forskolin, completely blocked IL-17-induced NO production. KT-5720, genistein, and Calphostin C, inhibitors of protein kinase A (PKA), tyrosine kinase, and protein kinase C, respectively, reduced the IL-17-induced NO production by 72%, 56%, and 42%, respectively. Within minutes, IL-17 induced the phosphorylation of mitogen-activated protein kinase kinase-1/2 (MEK-1/2), -3/6 (MKK-3/6), p44/42, p38, and inhibitor of nuclear factor kappaB (I kappaB)-alpha, as well as the activation of mitogen-activated protein kinase-activated protein kinase-1 and -2 (MAPKAPK-1 and -2). Interestingly, IL-17 induced phosphorylation of the stress-activated protein kinase/Jun N-terminal kinase (SAPK/JNK) (p54/46) only when PKA was inhibited. Specific protein kinase inhibitors for MEK-1/2 (PD98059), p38 (SB202190), and nuclear factor kappaB (NF-kappaB) (pyrrolidine dithiocarbamate) each markedly decreased the IL-17-increased iNOS level and NO production. Inhibiting MAPK, including MEK-1/2 and p38, had no effect on the IL-17-induced activation of IkappaB-alpha, but reversed the IL-17 activation of MAPKAPK-1 and -2, respectively.

CONCLUSION

These findings show that the stimulation of NO production by IL-17 is mediated mainly by a complex activation of kinases, especially PKA, NF-kappaB, and MAPK. NF-kappaB appears to require MAPK activation, with downstream activation of MAPKAPK probably acting as a transactivating factor, to induce iNOS expression.

Nitric oxide-releasing compounds inhibit neutrophil adhesion to endothelial cells

In the present work, we demonstrated that chemically different nitric oxide (NO)-releasing compounds inhibit tumor necrosis factor alpha (TNF-alpha)-induced polymorphonuclear leukocyte adhesion to endothelial cells in vitro. Two mesoionic oxatriazole derivatives GEA 3162 (1,2,3,4-oxatriazolium,5-amino-3(3, 4-dichlorophenyl)-chloride) and GEA 3175 (1,2,3,4-oxatriazolium, -3-(3-chloro-2-methylphenyl)-5-[[(4-methylphenyl)sulfonyl]amino]-, hydroxide inner salt) were compared to the earlier-known NO donor SIN-1 (3-morpholino-sydnonimine). GEA 3162 (3-10 microM) and GEA 3175 (10-30 microM) inhibited human polymorphonuclear leukocyte adhesion to B(4) endothelial cells in a dose-dependent manner being more potent than SIN-1. In the present model, leukocytes rather than endothelial cells seemed to be the target of the effect of NO. Flow cytometric analysis showed that NO-releasing compounds did not alter TNF-alpha induced CD11/CD18 surface expression in polymorphonuclear leukocytes. The inhibitory action of NO-releasing compounds on adhesion paralleled with the increased synthesis of cGMP in polymorphonuclear leukocytes. Analogues of cGMP inhibited polymorphonuclear leukocyte adhesion indicating a role for cGMP in the action of NO donors. The results suggest that exogenous NO in the form of NO-releasing compounds inhibits polymorphonuclear leukocyte adhesion to endothelial cells, which may be implicated in the regulation of leukocyte migration and leukocyte-mediated tissue injury.

Cartilage protection by nitric oxide synthase inhibitors after intraarticular injection of interleukin-1beta in rats

OBJECTIVE

To evaluate the effect of nitric oxide synthase (NOS) inhibitors on proteoglycan synthesis following intraarticular administration of interleukin-1beta (IL-1beta) in rats.

METHODS

Recombinant human IL-1beta and NOS inhibitors with different selectivity for inducible NOS (N-monomethyl-L-arginine [L-NMA], N-iminoethyl-L-ornithine [L-NIO], and S-methylisothiourea [SMT]) were simultaneously administered in rats by a single intraarticular injection in each knee. L-NMA was also infused for 72 hours using an Alzet mini osmotic pump implanted into the peritoneal cavity 24 hours before IL-1beta challenge. NO production was determined as nitrate and nitrite, either in synovial fluid or ex vivo in supernatants of synovium and patellae. Proteoglycan synthesis was measured by ex vivo incorporation of 35SO4(2-) into patellar cartilage.

RESULTS

IL-1beta induced a time-dependent increase in NO production in synovial fluid. Synovium and patellae released large amounts of nitrate and nitrite under ex vivo conditions, indicating that both tissues are effective sources of NO within the joint. This production of NO was accompanied by a delayed inhibition of proteoglycan synthesis. The intraarticular administration of L-NMA and L-NIO reduced NO release in synovial fluid and resulted in a partial recovery of proteoglycan synthesis. Under our experimental conditions, SMT failed to reduce NO synthesis and to restore proteoglycan synthesis. The protection of cartilage was improved by the systemic and sustained delivery of L-NMA. However, the complete inhibition of NO production in synovial fluid was not sufficient to fully restore cartilage anabolism.

CONCLUSION

Our findings show that in rats: 1) NO may be an early mediator of the effect of IL-1beta on cartilage, 2) NO inhibition may have therapeutic relevance, although it is not sufficient to fully reverse the deleterious effects of IL-1beta, 3) among NOS inhibitors tested, only amino acid derivatives are effective, 4) protection can be achieved by local administration of NOS inhibitors, and 5) systemic and sustained delivery of the NOS inhibitor with the highest efficacy after intraarticular injection provides the most benefit.

Modulation of IL-1 effects on cartilage by NO synthase inhibitors: pharmacological studies in rats

Objective To compare the ability of L-arginine (L-arg) analog nitric oxide synthase (NOS) inhibitors and isothioureas to restore the interleukin-1 (IL-1) induced inhibition of proteoglycan (PG) synthesis in rat.Methods Chondrocytes beads and patellae were challenged with IL-1betain vitro and monitored for NO production and proteoglycan synthesis. Rats injected with IL-1beta in knee joints were monitored for NO(2)( - )+NO(3)( - )levels in joint tissues and ex-vivo(35)S sulfate incorporation in patellae. NOS inhibitors were either added to culture medium or injected concomittantly to IL-1beta. Results Ability of NOS inhibitors to reduce NO(2)( - )levels decreased from chondrocytes beads to patellae. Partial restoration of PG synthesis was restricted to L-arg analogs in patellae. After IL-1 injection, NO was produced from patella and synovium. L-arg analogs restored partly PG synthesis when decreasing significantly NO(2)( - )+NO(3)( - )levels in synovial fluid. Isothioureas were ineffective. Conclusions NO accounts importantly for IL-1 induced inhibition of cartilage anabolism in rat. L-arg analog NOS inhibitors are more effective than isothioureas in restoring PG synthesis and have chondroprotective potency when administered locally in diseased joint.

Inhibition of transforming growth factor beta production by nitric oxide-treated chondrocytes: implications for matrix synthesis

OBJECTIVE

Nitric oxide (NO) is generated copiously by articular chondrocytes activated by interleukin-1beta (IL-1beta). If NO production is blocked, much of the IL-1beta inhibition of proteoglycan synthesis is prevented. We tested the hypothesis that this inhibitory effect of NO on proteoglycan synthesis is secondary to changes in chondrocyte transforming growth factor beta (TGFbeta).

METHODS

Monolayer, primary cultures of lapine articular chondrocytes and cartilage slices were studied. NO production was determined as nitrite accumulation in the medium. TGFbeta bioactivity in chondrocyte- and cartilage-conditioned medium (CM) was measured with the mink lung epithelial cell bioassay. Proteoglycan synthesis was measured as the incorporation of 35S-sodium sulfate into macromolecules separated from unincorporated label by gel filtration on PD-10 columns.

RESULTS

IL-1beta increased active TGFbeta in chondrocyte CM by 12 hours; by 24 hours, significant increases in both active and latent TGFbeta were detectable. NG-monomethyl-L-arginine (L-NMA) potentiated the increase in total TGFbeta without affecting the early TGFbeta activation. IL-1beta stimulated a NO-independent, transient increase in TGFbeta3 at 24 hours; however, TGFbeta1 was not changed. When NO synthesis was inhibited with L-NMA, IL-1beta increased CM concentrations of TGFbeta1 from 24-72 hours of culture. L-arginine (10 mM) reversed the inhibitory effect of L-NMA on NO production and blocked the increases in TGFbeta1. Anti-TGFbeta1 antibody prevented the restoration of proteoglycan synthesis by chondrocytes exposed to IL-1beta + L-NMA, confirming that NO inhibition of TGFbeta1 in IL-1beta-treated chondrocytes effected, in part, the decreased proteoglycan synthesis. Furthermore, the increase in TGFbeta and proteoglycan synthesis seen with L-NMA was reversed by the NO donor S-nitroso-N-acetylpenicillamide. Similar results were seen with cartilage slices in organ culture. The autocrine increase in CM TGFbeta1 levels following prior exposure to TGFbeta1 was also blocked by NO.

CONCLUSION

NO can modulate proteoglycan synthesis indirectly by decreasing the production of TGFbeta1 by chondrocytes exposed to IL-1beta. It prevents autocrine-stimulated increases in TGFbeta1, thus potentially diminishing the anabolic effects of this cytokine in chondrocytes.

Interleukin-1 induced nitric oxide inhibits sulphation of glycosaminoglycan chains in human articular chondrocytes

Incubation of human articular cartilage explants with interleukin-1alpha (IL-1alpha) inhibited the rate of [35S]sulphate incorporation into glycosaminoglycan (GAG) chains concomitant with an increase in nitric oxide (NO) production. Measurement of the [35S]sulphate showed that IL-1alpha inhibited the synthesis of both keratan sulphate and chondroitin sulphate (CS) chains to a similar extent. This effect was reversed by the NO synthase inhibitor Nomega-iminoethyl-l-ornithine (l-NIO). Analysis of alkali borohydride cleaved GAG chains showed that IL-1alpha had no effect on their size. Similarly when GAG chains were coupled to xyloside the size of the GAG chains attached to the exogenous acceptor decreased but IL-1alpha had no further effect on hydrodynamic size. IL-1alpha did, however, inhibit [35S]sulphate incorporation into xyloside-linked CS chains. In both experiments l-NIO reversed the inhibitory effect on sulphation. Disaccharide analysis of the [35S]GAG chains showed that IL-1alpha preferentially inhibited sulphation of the 6-sulphated isomer and that l-NIO reversed this effect. Thus, IL-1alpha-induced NO mediates the inhibition of sulphate incorporation and alters the sulphation pattern of newly synthesised GAG chains.

Inhibition by nitric oxide-releasing compounds of prostacyclin production in human endothelial cells

1. The effects of two chemically unrelated nitric oxide (NO)-releasing compounds were studied on prostacyclin production in lipopolysaccharide (LPS)-stimulated human umbilical vein endothelial cells (HUVECs). The cells expressed cyclooxygenase-2 (COX-2) protein and produced prostacyclin by NS-398-sensitive manner suggesting that prostacyclin production derives principally by COX-2 pathway. 2. A novel NO-releasing oxatriazole derivative GEA 3175 (1-30 microm) inhibited LPS-induced production of prostacyclin in HUVECs in a dose-dependent manner being more potent than the earlier known NO-donor S-nitroso-N-acetylpenicillamine (SNAP). 3. The effects of the two NO-donors on prostacyclin synthesis were reversed when red blood cells were added into the culture indicating that the effects are due to NO released from the compounds. 4. Addition of exogenous arachidonic acid into the culture did not alter the inhibitory action of NO-donors suggesting that phospholipases are not the target of action of NO. 5. The NO-donors did not inhibit prostacyclin production in the presence of a selective COX-2 inhibitor NS-398. These data suggest that NO affects COX-2 pathway rather than has an overall effect on cyclooxygenases. 6. NO-releasing compounds did not alter the level of COX-2 protein expression in LPS-treated HUVECs as measured by Western blot analysis. 7. The results suggest that NO-donors inhibit the activity of COX-2 in human endothelial cells. A link between NO and the regulation of eicosanoid synthesis could represent an important mechanism in controlling vascular and inflammatory responses in pathophysiological states and during treatment with nitrovasodilators.

Modulation of IL-1-induced cartilage injury by NO synthase inhibitors: a comparative study with rat chondrocytes and cartilage entities

Nitric oxide (NO) is produced in diseased joints and may be a key mediator of IL-1 effects on cartilage. Therefore, we compared the potency of new [aminoguanidine (AG), S-methylisothiourea (SMT), S-aminoethylisothiourea (AETU)] and classical [Nomega-monomethyl-L-arginine (L-NMMA), Nomega-nitro-L-arginine methyl ester (L-NAME)] NO synthase (NOS) inhibitors on the inhibitory effect of recombinant human interleukin-1beta (rhIL-1beta) on rat cartilage anabolism. Three different culture systems were used: (1) isolated chondrocytes encapsulated in alginate beads; (2) patellae and (3) femoral head caps. Chondrocyte beads and cartilage entities were incubated in vitro for 48 h in the presence of rhIL-1beta with a daily change of incubation medium to obtain optimal responses on proteoglycan synthesis and NO production. Proteoglycan synthesis was assessed by incorporation of radiolabelled sodium sulphate [Na2(35)SO4] and NO production by cumulated nitrite release during the period of study. Chondrocytes and patellae, as well as femoral head caps, responded concentration-dependently to IL-1beta challenge (0 to 250 U ml(-1) and 0 to 15 U ml(-1) respectively) by a large increase in nitrite level and a marked suppression of proteoglycan synthesis. Above these concentrations of IL-1beta (2500 U ml(-1) and 30 U ml(-1) respectively), proteoglycan synthesis plateaued whereas nitrite release still increased thus suggesting different concentration-response curves. When studying the effect of NOS inhibitors (1 to 1000 microM) on NO production by cartilage cells stimulated with IL-1beta (25 U ml(-1) or 5 U ml(-1)), we observed that: (i) their ability to reduce nitrite level decreased from chondrocytes to cartilage samples, except for L-NMMA and AETU; (ii) they could be roughly classified in the following rank order of potency: AETU > L-NMMA > or = SMT > or = AG > or = L-NAME and (iii) AETU was cytotoxic when used in the millimolar range. When studying the effect of NOS inhibitors on proteoglycan synthesis by cartilage cells treated with IL-1beta, we observed that: (i) they had more marked effects on proteoglycan synthesis in chondrocytes than in cartilage samples; (ii) they could be roughly classified in the following rank order of potency: L-NAME > or = L-NMMA > > AG > SMT > > AETU and (iii) potentiation of the IL-1 effect by AETU was consistent with cytotoxicity in the millimolar range. D-isomers of L-arginine analog inhibitors (1000 microM) were unable to correct nitrite levels or proteoglycan synthesis in IL-1beta treated cells. L-arginine (5000 microM) tended to reverse the correcting effect of L-NMMA (1000 microM) on proteoglycan synthesis, thus suggesting a NO-related chondroprotective effect. However, data with L-NAME and SMT argued against a general inverse relationship between nitrite level and proteoglycan synthesis. Dexamethasone (0.1 to 100 microM) (i) failed to inhibit NO production in femoral head caps and chondrocytes beads whilst reducing it in patellae (50%) and (ii) did not affect or worsened the inhibitory effect of IL-1beta on proteoglycan synthesis. Such results suggested a corticosteroid-resistance of rat chondrocyte iNOS. Data from patellae supported a possible contribution of subchondral bone in NO production. In conclusion, our results suggest that (i) NO may account only partially for the suppressive effects of IL-1beta on proteoglycan synthesis, particularly in cartilage samples; (ii) the chondroprotective potency of NOS inhibitors can not be extrapolated from their effects on NO production by joint-derived cells and (iii) L-arginine analog inhibitors are more promising than S-substituted isothioureas for putative therapeutical uses.

Reduced progression of experimental osteoarthritis in vivo by selective inhibition of inducible nitric oxide synthase

OBJECTIVE

To evaluate the in vivo therapeutic efficacy of N-iminoethyl-L-lysine (L-NIL), a selective inhibitor of inducible nitric oxide synthase (iNOS), on the progression of lesions in an experimental osteoarthritis (OA) dog model. The effect of L-NIL on metalloprotease activity, levels of interleukin-1beta (IL-1beta), prostaglandin E2 (PGE2), and nitrite/nitrate in synovial fluid was determined.

METHODS

The OA model was created by sectioning the anterior cruciate ligament of the right stifle joint of mongrel dogs by a stab wound. Dogs were separated into experimental groups: Group 1 was made up of unoperated dogs that received no treatment, group 2 were operated dogs with no treatment, and group 3 were operated dogs that received oral L-NIL (10 mg/kg/twice daily) starting immediately after surgery. The OA dogs were killed at 10 weeks after surgery.

RESULTS

Experiments showed that dog OA cartilage explants in culture produced an increased amount of NO (nitrite). Immunohistochemical study demonstrated that this was due to an increased level of iNOS in chondrocytes. OA dogs treated with L-NIL showed a reduction in the incidence of osteophytes compared with the untreated OA dogs (58% versus 92%) as well as in their size (mean +/- SEM 1.92 +/- 0.58 mm versus 5.08 +/- 0.66 mm). Macroscopically, L-NIL decreased the size of the cartilage lesions by approximately 50% both on condyles and plateaus. The histologic severity of both the cartilage lesions and synovial inflammation was significantly decreased in the L-NIL-treated dogs. Treatment with L-NIL also significantly decreased both collagenase and general metalloprotease activity in the cartilage and the levels of IL-1beta, PGE2, and nitrite/nitrate in synovial fluid.

CONCLUSION

This study demonstrated the effectiveness of a selective inhibitor of iNOS, L-NIL, in attenuating the progression of experimental OA. The data suggest that L-NIL may act by reducing the activity of metalloproteases in cartilage and the production of IL-1beta by synovium, both of which are known to play a major role in the pathophysiology of OA structural changes.

SB 203580 Inhibits p38 Mitogen-Activated Protein Kinase, Nitric Oxide Production, and Inducible Nitric Oxide Synthase in Bovine Cartilage-Derived Chondrocytes

Nitric oxide (NO) is implicated in a number of inflammatory processes and is an important mediator in animal models of rheumatoid arthritis and in in vitro models of cartilage degradation. The pyridinyl imidazole SB 203580 inhibits p38 mitogen-activated protein (MAP) kinase in vitro, blocks proinflammatory cytokine production in vitro and in vivo, and is effective in animal models of arthritis. The purpose of this study was to determine whether SB 203580 could inhibit p38 MAP kinase activity, NO production, and inducible NO synthase (iNOS) in IL-1 stimulated bovine articular cartilage/chondrocyte cultures. The results indicated that SB 203580 inhibited both IL-1 stimulated p38 MAP kinase activity in isolated chondrocytes and NO production in bovine chondrocytes and cartilage explants with an IC50 value of approximately 1 μM. To inhibit NO production, SB 203580 had to be present in cartilage explant cultures during the first 8 h of IL-1 stimulation, and activity was lost when it was added 24 h following IL-1. SB 203580 did not inhibit iNOS activity, as measured by the conversion of arginine to citrulline, when added directly to cultures where the enzyme had already been induced, but had to be present during the induction period. Using a 372-bp probe for bovine iNOS we demonstrated inhibition of IL-1-induced mRNA by SB 203580 at both 4 and 24 h following IL-1 treatment. The iNOS mRNA levels were consistent with NO levels in 24-h cell culture supernatants of the IL-1-stimulated bovine chondrocytes used to obtain the RNA.

Expression of decorin and biglycan by rabbit articular chondrocytes. Effects of cytokines and phenotypic modulation

In this study, the levels of mRNAs coding for aggrecan, decorin and biglycan in rabbit articular chondrocytes were investigated, using both monolayer and 3D-alginate cultures treated with TGF-beta 1 and IL-1 beta. The cells were shown to express higher amounts of proteoglycan messages, specially the aggrecan, in gels than in monolayers. TGF-beta 1 increased aggrecan mRNA in both systems, whereas biglycan message was elevated only in alginate. It markedly decreased decorin expression in monolayer, either in primary or passaged cultures. In contrast, IL-1 beta had a weak inhibitory effect on both decorin and biglycan expression. Subculturing induced a dramatic decrease of aggrecan mRNA, while that of decorin augmented. Biglycan expression transiently increased after two passages, whereas it declined in further subcultures. Passaged chondrocytes transferred to alginate re-expressed high levels of aggrecan, decorin and biglycan. The data point to the influence of morphology, proliferative state and environment of the articular chondrocytes on their biosynthetic responses to cytokines. Although these immature cells do not fully reflect the adult chondrocytes present in the cartilage, this study may help in understanding the behaviour of these cells in osteoarticular diseases, where the surrounding extracellular matrix is profoundly altered.

Reduced cartilage proteoglycan loss during zymosan-induced gonarthritis in NOS2-deficient mice and in anti-interleukin-1-treated wild-type mice with unabated joint inflammation

OBJECTIVE

To investigate the role of nitric oxide (NO) and interleukin-1 in (IL-1) joint inflammation and cartilage destruction during zymosan-induced gonarthritis (ZIA).

METHODS

Monarticular arthritis was elicited by intraarticular injection of zymosan. The effect of NO deficiency on arthritis was studied in mice with genetically disrupted NOS2. The role of IL-1 was examined by treating wild-type mice with neutralizing anti-murine IL-1(alpha+beta) antibodies. Joint swelling was measured externally by the increased uptake of circulating 99mtechnetium pertechnetate. Proteoglycan (PG) synthesis was assessed using 35S-sulfate incorporation into patellae ex vivo. Histology evaluated exudation and infiltration of leukocytes and the extent of cartilage destruction.

RESULTS

The proinflammatory mediators NO, IL-1, and IL-6 were released by the articular tissues during the first hours of inflammation. Interestingly, anti-IL-1 treatment moderately reduced, and NOS2 deficiency moderately enhanced, joint swelling. However, the influx of neutrophils into the joint occurred independently of IL-1 and NOS2 activities. In the first week of inflammation, chondrocyte PG synthesis was significantly suppressed and chondrocytes became unresponsive to their essential anabolic factor, insulin-like growth factor 1 (IGF-1). Anti-IL-1 treatment or NOS2 deficiency prevented the inhibition of PG synthesis, and the chondrocytes remained IGF-1 responsive. Intraarticular injections of IL-1alpha into NOS2-deficient mice did not affect PG synthesis, thus proving that NO mediated this IL-1 effect in vivo. Furthermore, histology showed that cartilage PG loss was markedly ameliorated in NOS2-deficient and anti-IL-1-treated mice. Intermediate cartilage pathology was found in mice that were heterozygous for disrupted NOS2.

CONCLUSION

IL-1 and NO play a minor role in edema and neutrophil influx, but a major role in cartilage destruction of ZIA. In this model of murine arthritis, cartilage destruction was, for the most part, caused by pronounced suppression of PG synthesis and IGF-1 unresponsiveness of the chondrocytes, which were induced by de novo-synthesized IL-1 and were mediated by NOS2 activation.

Differences in Nitric Oxide Production by Superficial and Deep Human Articular Chondrocytes: Implications for Proteoglycan Turnover in Inflammatory Joint Diseases

During inflammatory joint diseases, chondrocytes are exposed to cytokines such as IL-1 that induce the synthesis of nitric oxide (NO). Chondrocytes from different zones of the articular cartilage are known to have different metabolic properties. In the present study, we have demonstrated that chondrocytes recovered from the superficial zone of normal, human, articular cartilage synthesize approximately 2 to 3 times as much NO in response to IL-1 as chondrocytes recovered from the deep zone of the same cartilage. Production of NO by normal cartilage in response to IL-1 was also found to decrease with age. Addition of the NO synthase inhibitor NG-monomethyl-l-arginine (l-NMA, 1 mM) blocked NO production by cells of both zones. l-NMA completely reversed the suppression of proteoglycan synthesis imposed by IL-1 in deep chondrocytes, but produced only partial reversal in superficial cells. As noted previously, IL-1 failed to elicit a strong catabolic response in cultures of human cartilage. In the presence of l-NMA, however, IL-1 reduced the metabolic t1/2 of proteoglycans by approximately 50% in both the superficial and deep zones. This suggests that NO has, directly or indirectly, an anticatabolic effect in human cartilage. These data confirm the metabolic heterogeneity of human chondrocytes, and suggest that NO may be involved to different degrees as an endogenous modulator of the turnover of the cartilaginous matrix in different zones of articular cartilage.

Generation of nitric oxide by lapine meniscal cells and its effect on matrix metabolism: stimulation of collagen production by arginine

Slices of lapine meniscus produced large amounts of nitric oxide after stimulation with interleukin-1, tumor necrosis factor alpha, or a mixture of lapine synovial cytokines known as chondrocyte-activating factors. Monolayer cultures of meniscal cells produced from the proteolysis of meniscal tissue contained a mixed population of chondrocytic and fibroblastic cells. These cultures also produced large amounts of nitric oxide in response to cytokines. Monolayer cultures of meniscal cells produced by the explant method, in contrast, were uniformly fibroblastic and did not produce nitric oxide in response to cytokines. We conclude that menisci contain two populations of cells, one fibroblastic and the other chondrocytic. The chondrocytic cells are responsible for generating most of the nitric oxide in response to cytokines. Endogenously generated nitric oxide suppressed the synthesis of collagen and proteoglycan by menisci but protected proteoglycan from the catabolic effects of interleukin-1. The inhibitory effect of nitric oxide on collagen synthesis occurred without greatly altering the abundance of mRNAs encoding the various collagen alpha chains. During further investigation, arginine was unexpectedly found to stimulate the synthesis of collagen and, to a lesser degree, of noncollagenous proteins but not of proteoglycans. Fragments of meniscus, but not meniscal cells in monolayer culture, increased their production of matrix metalloproteinases, lactate, and, especially, prostaglandin E2 in response to interleukin-1. Inhibition of nitric oxide production with NG-monomethyl-L-arginine enhanced production of matrix metalloproteinases but had little effect on the synthesis of lactate or prostaglandin E2.

Inhibition of human lymphocyte proliferation by nitric oxide-releasing oxatriazole derivatives

The effects of novel nitric oxide (NO)-releasing oxatriazole derivatives GEA 3162 and GEA 3175 were studied on cell proliferation and cGMP synthesis in human peripheral blood mononuclear cells stimulated with a lectin mitogen concanavalin A. GEA 3162 (1-30 microM) and GEA 3175 (3-30 microM) inhibited mononuclear cell proliferation in a dose-dependent manner being more potent than the earlier known NO-donor S-nitroso-N-acetylpenicillamine. The inhibitory action was more pronounced when submaximally stimulating concentrations of concanavalin A (0.1 and 1 microg/ml) were used and no inhibition was seen when concanavalin A concentrations were increased up to 10 microg/ml. The antiproliferative concentrations of GEA 3162, GEA 3175 and S-nitroso-N-acetylpenicillamine induced a rapid and transient increase in cGMP production in mononuclear cells cultured in the presence of concanavalin A. Both the antiproliferative action and the increased cGMP production were attenuated when red blood cells were added into the cultures indicating that NO is responsible for both of these actions. An analogue of cGMP, 8-bromo-cGMP (0.1-3 mM) reduced concanavalin A-induced proliferation in a dose-dependent manner suggesting that cGMP may be involved in the antiproliferative action of NO-donors. NO-releasing compounds have immunosuppressive actions which offer therapeutic possibilities and should be kept in mind as potential adverse events when these compounds are used in other indications.

Nitric oxide and proteoglycan turnover in rabbit articular cartilage

Articular chondrocytes are known to synthesize large amounts of nitric oxide in response to exposure to interleukin-1, but the role of this radical in proteoglycan turnover remains controversial. In this study, we used two different inhibitors of nitric oxide synthase, NG-methyl-L-arginine and thiocitrulline, to study the effects of nitric oxide on the synthesis and breakdown of proteoglycan in rabbit articular cartilage. Synthesis of nitric oxide by cartilage slices in response to treatment with interleukin-1 and a partially purified mixture of synovial cytokines known as chondrocyte-activating factors peaked during the first 2 days of culture and then fell to low levels, despite daily replenishment with fresh medium and cytokines to the cultures. The production of nitric oxide was completely inhibited by NG-methyl-L-arginine and thiocitrulline. Interleukin-1 and the chondrocyte-activating factors inhibited proteoglycan synthesis and accelerated proteoglycan breakdown in the slices of cartilage. Both nitric oxide synthase inhibitors substantially counteracted the suppression of proteoglycan synthesis but exacerbated proteoglycan catabolism occurring in response to interleukin-1 and the chondrocyte-activating factors. The accelerated catabolism was associated with increased levels of matrix metalloproteinases in the conditioned medium. This dual effect of nitric oxide complicates decision making with regard to the possible clinical applications of nitric oxide agonists or antagonists in diseases of cartilage.

Nitric oxide production by equine articular cells in vitro

Recent research in several species has suggested nitric oxide (NO) as a mediator of articular cartilage damage and an inhibitor of cartilage matrix neosynthesis. This study investigated NO production by cultured equine articular chondrocytes in response to 2 arthritogenic molecules, namely lipopolysaccharide (LPS) and interleukin-1 beta (IL-1 beta), and compared NO production by cultured equine synoviocytes stimulated with LPS. Synoviocytes exhibited a low basal level of NO synthesis (measured as nitrite, a NO metabolite) that was neither significantly increased nor decreased by exposure to LPS. Basal NO synthesis by synoviocytes was not significantly reduced by competitive inhibitors of nitric oxide synthase (NOS). In contrast, chondrocytes treated with LPS or IL-1 beta synthesised nitrite in a dose-related manner. Inhibitors of NOS suppressed nitrite production to below the basal levels of release of unstimulated cells. Dexamethasone, an inhibitor of induction of the inducible isoform of NOS (iNOS), reduced nitrite synthesis by LPS-stimulated chondrocytes. Western blot analysis revealed expression, in response to LPS, of protein in the same molecular weight range as iNOS identified in other species. This work demonstrates that equine chondrocytes have the capacity to synthesise NO, although its exact roles in cartilage metabolism have yet to be determined.

Endogenous nitric oxide and prostaglandin E2 do not regulate the synthesis of each other in interleukin-1 beta-stimulated rat articular cartilage

Increased levels of nitric oxide (NO) and prostaglandins (PG) are present in the synovial fluid from patients with rheumatoid arthritis and osteoarthritis. Interleukin-1 beta (IL-1) has been shown to induce the synthesis of both of these mediators. The present work was designed to study the interactions of NO and PGE2 synthesis induced by IL-1 in rat articular cartilage. Incubation of intact cartilage with IL-1 resulted in different dose response curves for NO and PGE2 synthesis. Two inhibitors of nitric oxide synthase N-monomethyl-L-arginine (L-NMMA) and L-N-iminoethylornithine, (L-NIO), abolished the IL-1-induced nitrite production but failed to have any influence on the PGE2 synthesis. Exogenous NO, produced by two chemically different NO-releasing compounds (SIN-1 and GEA 3175) had no effect on PGE2 synthesis in articular cartilage. Dexamethasone and ketoprofen inhibited IL-1 induced PGE2 production, while nitrite synthesis remained unaltered. Acetylsalicylic acid (ASA) reduced PGE2 synthesis and had a slight inhibitory action also on NO production. In conclusion, our results show, that IL-1 induces the synthesis of both PGE2 and NO in articular cartilage but these two inflammatory mediators are not mediating the synthesis of one another.

Articular cartilage destruction in experimental inflammatory arthritis: insulin-like growth factor-1 regulation of proteoglycan metabolism in chondrocytes

Rheumatoid arthritis, a disease of unknown aetiology, is characterized by joint inflammation and, in its later stages, cartilage destruction. Inflammatory mediators may exert not only suppression of matrix synthesis but also cartilage degradation, which eventually leads to severe cartilage depletion. Systemically and locally produced growth factors and hormones regulate cartilage metabolism. Alterations in levels of these factors or in their activity can influence the pathogenesis of articular cartilage destruction in arthritic joints. The main topic of the present review is the role of the anabolic factor insulin-like growth factor-1 in the regulation of chondrocyte metabolic functions in normal and in diseased cartilage. This is the most important growth factor that balances chondrocytes proteoglycan synthesis and catabolism to maintain a functional cartilage matrix. A brief overview of how chondrocytes keep the cartilage matrix intact, and how catabolic and anabolic factors are thought to be involved in pathological cartilage destruction precedes the review of the role of this growth factor in proteoglycan metabolism in cartilage.